Elevator control including a common transmission circuit with a threshold circuit for each car to determine its availability to answer calls



Ma mm m m D D p 1968 M. c. YEASTING ELEVATOR CONTROL INCLUDING A COMMON TRANSMISSION CIRCUIT WITH A THRESHOLD CIRCUIT FOR EACH CAR TO DETERMINE ITS AVAILABILITY TO ANSWER CALLS Filed March 26, 1963 6 Sheets-Sheet m n. m m w m. s 6 $549 biz.

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ELEVATOR CONTROL INCLUDING A COMMON TRANSMISSION CIRCUIT WITH A THRESHOLD CIRCUIT FOR EACH CAR TO DETERMINE ITS AVAILABILITY TO ANSWER CALLS Filed March 26, 6 Sh t s t 6 'lg uua 25 0%) DLC I I220 F E -22| R, [Q

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"4 I klgJO MAYNARD c. YEASTING dilqrneys United States Patent ELEVATGR CONTROL INCLUDING A COMMON TRANSMISSION CIRCUIT WITH A THRESHGLD CIRCUIT FOR EACH CAR Ti) DETERMENE ITS AVAlLAElLlTY TO ANSWER CALLS Maynard C. Yeasting, Elmore, Ohio, assignor, by mesne assignments, to T he Reliance Electric and Engineering Company, (Ileveland, Ohio, a corporation of Ghio Filed Mar. 26, 1953, Ser. No. 268,023 7 Claims. (Cl. 187-49) This invention relates to elevator supervisory control systems and in particular to a group supervisory control for selecting and starting elevator cars in response to calls for service.

In presently known group supervisory control systems the control system is responsive to the registration of a hall call to start the car or cars responsible for the zone of fioors from which the call originated. The number of cars brought into service and the program of operation is usually determined by the time intervals elapsing between elevator operations such as the opening or closing of the doors or the starting or stopping of the cars and the elevator service is distributed among the various floors by causing the cars to operate generally in round trip fashion between the terminals or between one of the terminals and the furthest registered call. The service is further distributed by releasing the cars from one or more points in the system at generally uniform intervals of time in which the duration of the intervals is varied according to the magnitude of the demand for service. Such a system does not make maximum use of available elevator facilities because cars are often held at the terminal floors for dispatching while passengers are waiting for service at intermediate floors.

The principal object of this invention is to provide a group supervisory control system in which the elevator cars operate between the lowest call or a particular floor such as a lobby and the furthest registered call from that floor and in which no car is started into operation or continued in operation unless it is serving a car call, i.e. a call registered by a passenger within the car, or there is a hall call registered which the car can probably reach ahead of any other car in the system.

Another object of the invention is to provide a simple group supervisory control system in which an idle car near a call will not respond if there is a car in use and in position to promptly service the call.

Another object of the invention is to provide a group supervisory control system for a group of elevators in which an idle elevator car is instantly started in operation upon the registration of a predetermined number of calls ahead of a preceding car.

Another object of the invention is to provide a group supervisory control system in which a moderately loaded car bypasses a registered hall call whenever there is a following lightly loaded car or an idle car in position to prompty answer the hall call.

Another object of the invention is to provide a group supervisory control system which is readily adjustable for matching its characteristics to the tratlic demands of a particular building.

Another object of the invention is to provide a group supervisory control system in which a basement serving car is promptly selected and called into operation immediately upon the registration of a call requiring service to the basement.

These and other objects and advantages are provided by a supervisory control system constructed and operated according to the invention.

According to the invention signals corresponding to registered hall calls are supplied to a transmission circuit at points corresponding to the locations of the hall 3,379,284 Patented Apr. 23, 1968 calls and the signals are accepted and taken from the transmission circuit at points corresponding to the locations of the cars available for servicing the calls. Sensing circuits for each of the cars which are responsive to the condition of the car accept signals from the transmission circuit corresponding to hall calls that the car can answer and reject any further signals, whereby each of the cars through its sensing circuits takes from the transmission circuit signals corresponding only to those calls that the car is in condition to answer. The rejected sig nals are transmitted to other cars so that no car may remain idle while there is an excess of calls ahead of another car. Signals rejected by all the cars, indicating a heavy hall call load, initiate action to distribute the available service to all floors. Signals are also transmitted through the sensing circuits to call cars to the lobby according to demand and to select the car to be loaded at the lobby.

Essentials of a group supervisory control system constructed according to'the invention are illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a diagrammatic illustration of a group of elevators arranged to serve a plurality of floors.

FlGURE 2 is a schematic circuit diagram of circuits suitable for registering hall calls and initiating stops of the elevator cars at the floors corresponding to the calls.

FIGURE 3 is a schematic diagram of circuits suitable for controlling the direction of travel of the car in response to calls for service.

FIGURES 4 and 4A are schematic diagrams of circuits suitable for registering car calls and initiating stops of the elevator car in response to car calls or sensed hall calls.

FIGURE 5 is a schematic wiring diagram of the hall call transmission circuit indicating its connection to the hall call registering means and to the signal sensing circuits of each of the elevator cars.

FIGURE 6 is a schematic wiring diagram of one of the sensing circuits for one of the elevator cars.

FIGURE 7 is a graph illustrating the operating characteristics of the signal sensing circuits whereby the sensing circuit accepts signals only when its car is in condition to service the corresponding calls.

FIGURE 8 is a schematic diagram of the car starting circuit to illustrate the conditions under which the car will start into operation.

FIGURE 9 is a schematic diagram of certain relay circuits which in cooperation with the circuits of FIGURES 5 and 6 provides for return of cars to the lobby and selection of a car at the lobby floor for loading when there is a plurality of cars at the floor.

FIGURE 10 is a schematic diagram of a high call reverse circuit including means for varying the high call reverse point of the elevator cars to progressively lower the reversal point as the calls are cleared.

These specific figures and the accompanying description are intended merely to illustrate the invention and not to impose limitations on its scope.

GENERAL DESCRIPTION The supervisory control system according to the invention is concerned primarily with the selection and starting of elevator cars to service hall calls as they are registered. it is assumed that each car will promptly service any car calls that may be registered Within the car. The system responds to and provides maximum service in any traffic conditions from the extremely light intermittent tratfic that occurs in the ordinary office building at night or during holidays to the extremely heavy uppeak or downpeak traflic which occurs at the beginning and close of each business day.

The principal feature of the improved group supervisory control system is that any registered call for service is transmitted directly to the elevator car in position to serve the floor at which the call is registered. If the car is in condition to accept a call that car is started in operation to answer the call and nothing further happens in the system. However if that car is not in condition to accept a call the call is transmitted to the car in the next best position and so on until a car is found which can service the call. The cars may be classified and their current status determined according to their condition or availability to accept calls for service into several orders or classes. These classes are (a) active, (b) idle, (c) half load, (d) reserve, and (e) special.

A special car is one not available for answering hall calls either by reason of being shut down for repair, in use for special services, or fully loaded on either an up trip or a down trip. Such a car will not accept any hall calls for service.

A reserve car is a car that is available for service except that its motor generator set is shut down. A reserve car is selected for answering a hall call in the event no other cars in the system are then available for answering the call.

A half loaded car is a car that is loaded to approximately 50% of its capacity. Such a car may be arranged to bypass hall calls in its direction of travel when there is a lightly loaded car or an idle car in position to promptly answer the calls.

An idle car is a car that has served its last car call and the timing interval for its motor generator set shut down has not expired.

An active car is a car that has accepted and has started to answer a hall call or a car call and that has not as yet acquired a half load.

For maximum service the system is preferably adjusted so that each car is responsible for the calls ahead of it and behind the preceding car. In the case of idle and reserve cars, since they may go either way as required, the calls ahead are the calls between the car and the next higher or the next lower car. Active and half loaded cars are responsible only for calls ahead in their direction of travel. In the preferred form the circuits are adjusted so that an active car accepts two hall call signals until it makes its first stop and thereafter accepts one hall call signal. Any signals resulting from further hall calls ahead of an active car are rejected and therefore transmitted to the next car. Furthermore, to conserve elevator travel, an active car having no hall calls between itself and a preceding idle car that is not more than a given number of floors ahead accepts a call ahead of the idle car.

The sensing circuits for the various cars also select the cars for loading at the lower terminal or lobby by providing that one car, an up lobby car, stands at the lobby conditioned for upward travel with its doors open to receive passengers and that any other cars arriving at the lobby have no directional preference and may close their doors immediately upon discharge of their passengers. Upon the registration of a car call in the up direction lobby car another car is called to the lobby if there is no second car already present. Upon the departure of the up lobby car the remaining car at the lobby, or one if there is more than one, is selected and becomes the up lobby car to receive lobby passengers. Selection is made from among the cars at the lobby according to the sensitivity of their respective sensing circuits which, although designed generally for the same sensitivity, have individual variations such that one responds to the exclusion of the others to a simultaneously applied signal. The departure of a car from the lobby is delayed for a brief time interval after each passenger entry unless the car is fully loaded or there is another car at the lobby. Thus the lobby car waits for a short predetermined time interval after each passenger entry to determine if there are other passengers waiting for travel and then departs provided the car has acquired a full load or there is another car at the lobby ready to assume loading condition. If desired an additional timer may be provided to allow the car to depart at the expiration of a longer predetermined time interval even though the car has neither acquired a full load nor has another car arrived at the lobby.

The system also provides, in the event less than all of the cars serve the basement, that, upon the registration of a call requiring basement service, the basement serving car or one of the basement serving cars is immediately selected and it thereupon proceeds toward the basement. It may, if desired, be given half load status after being selected for basement service thereby bypassing down calls as long as there is a following car or idle car in condition to promptly answer such calls.

During down peak trafiic conditions it often happens that cars become fully loaded at the upper floors of a building and then bypass intending passengers at lower floors. Thus passengers at intermediate and lower floors have to wait an unduly long time before they receive any service while the upper floors of the building have been repeatedly served. The supervisory control system recognizes and meets this problem by providing that, in the event there are not enough cars available to accept the signals of registered down calls, a sweeping operation is initiated in which the up travel of the cars is limited to the highest call below the last answered call. The up travel limit or ceiling is lowered to the next call as such highest call is answered thus progressing downwardly through the building in an orderly fashion as the calls are answered. When there are no remaining calls below the ceiling it starts over at the top of the building. Because a nearly fully loaded car may stop at an intermediate floor thereby canceling the call and shifting the ceiling for a lower floor and still be unable to accept all of the waiting passengers at such floor the circuits of the cars are arranged so that a half loaded down traveling car bypasses the call at the ceiling and completes its load at lower floors. Thus the call at the up travel limit or ceiling is always answered by a car having less than a half load and therefore presumably in condition to accept all of the Waiting passengers.

.Referring now to the accompanying drawings and in particular FIGURE 1, an elevator system to which the invention may be applied comprises a plurality of elevator cars 20 that serve a plurality of floors in response to signals registered by actuation of ball call buttons 21 or car calls registered by operation of destination buttons in each of the cars. The car buttons are not shown in FIG 1. but their contacts appear in lines 151 and 153 of FIG. 4A. The cars 20 are suspended by cables 22 which pass over sheaves or pulleys 23 and are connected to counterweights 24. The sheaves are mounted on armature shafts 25 of drive motors 26. The armature shafts 25 are also mechanically connected to fioor selector machines 27 which in cooperation with the call registering circuits and control circuits, not shown, control the operation of the elevator motors 26 to move the cars from floor to floor as may be required.

In the wiring diagrams the relays are given letter designations which under certain circumstances may also include a number. For example, those relays which are repeated for each floor of the building have designations which include the number of the corresponding floor. Certain relays which operate in sequence may also include numbers as part of the designation. Furthermore, since there can be no confusion between the symbol for contacts and the symbols for operating coils, the contacts operated by a given coil are given the same reference characters as the coil. The contacts operated by the coils are listed in a code along the right side of the figures in line with the operating coils. An underscored line number indicates that the corresponding contacts are closed when the coil is de-energized.

The relays or relay contacts appearing in the drawings and relay coil locations are as follows:

BC Basement Gall BK Brake C3, G7, etc Gar Calls 151,153 013.... Oar Call Above 141 GB Car Call Below. 149 00-- Car Call Count 150 03.. Car Start 212 DF Down Field DHO, DHCQ Down Hall Call Ahead 184,186 DL Down Direction DLO Down Lobby Car... 220 DO... Door Opening DRO Door Reopening 114 Gate HOR High Call Rover 244 HLBP- Hall Load Bypass.

. In Service Sweep-Stepping Relay... Up Hall Call UF.. Up Field UL Up Direction 127 UHO, UI-ICQ Up Hall Call Ahead V, VRl, VRZ Stopping Sequence FIGURES 2 and 3 Circuits for registering hall calls and for initiating stops in response to hall calls are illustrated in FIG. 2 These circuits include hall call relays SllU, S11U, 811D, 312D that are representative of the hall call storing relays, there being one for each terminal floor and two for each intermediate floor. These relays are of the mechanical or magnetic latch type and are arranged to be operated to an energized condition to close their normally open contacts whenever 'a corresponding hall button 21 is pressed and to be tuilatched or reset when the call is answered. Thus, an intending passenger at the eleventh floor desiring down transportation presses the down hall button 21 at the 11th floor. This action closes contacts marked 11D in line 103 to energize hall c'all relay S11D by current flow from a supply lead L1 through the energizing coil of the relay 511D in line 194, through the now manually closed contacts 11D in line 103 and thence through a lead 30 connected to a return line L2. As soon as a floor or hall call relay is energized it closes its corresponding contacts appearing along the left lower portion of FIG. 2. as well as opening or closing its contacts appearing in the supervisory circuits of FIGS. 5, 6, and 1 0.

The closure of the contacts S1.1D in line 112 prepares a circuit to selector machine segments 31, there being one for each elevator as indicated by the arrows 32, which co-operate with selector machine down stop brushes 33 so that when the selector machine brush 33 of a down traveling car contacts the energized segment 31 current may flow from the lead L1 through the brush 33, down direction contacts DL, normally closed stopping sequence relay contacts VRZ, load by-pass contacts LBP, h'alf load bypass contacts HLBP, coil S of the stopping relay, and normally open but now closed brake relay contacts BK to return lead L2. The load by-pass contacts LBP open when the car becomes loaded. The half load bypass contacts HLBP open when the car acquires a half load to shift the stopping control to the signal sensing circuit so that the hall call will be bypassed it there is a following empty or lightly loaded car or an idle car in position to promptly answer the call. If there is no lightly loaded following or'idle car contacts UHC or DHC in lines 110 or 111 are closed to complete the stopping circuit. This bypassing of calls by a half loaded car expedites service during light and medium traflic demands by shifting the loads away from the half loaded cars. The stopping relay S, by closing its contacts in line 132 of FIG. 4, prepares a circuit to energize stopping relay V as soon as a down stopping brush 34 contacts the corresponding now energized selector machine segment 35 as the selector machine moves its brushes toward a position corresponding to the eleventh floor. Energization of the stopping relay V starts a relay sequence which includes operation of relays VR, VR-l, and VR2. Relay VRl, by closing its contacts in line 109, completes a holding circuit for the now energized stop ping relay S. Stopping relay VR, included in this chain of stopping sequence relays by closing its contacts in line 104, completes a circuit to the reset coil of the eleventh floor down hall call relay 811D by way of the contacts appearing in line 104 thus resetting the relay to its unenergized or de-energi-zed condition. This is the indication that the call has been answered. Gate relay contacts G, closed only when the doors are open, complete the circuit to cancel hall calls at the floor while the car is still there. This action also energizes a call compensator relay K, line 190, which cooperates with the sensing circuits.

Simultaneously, the stopping sequence relay VRZ by opening its contacts in line 112 prevents any feedback of power from the lead L1 by way of the holding circuit contacts VRl and S in line 199 to the brush 33 so as to continue the energization of the down stopping selector machine segments 31 for other elevators which would stop any other down traveling cars if they approached the eleventh floor while the first car was decelerating to its stop. Thus, unless two cars are running exactly abreast, only the first car to receive the signal stops for the call.

Similar operation for up hall calls is provided by the up hall call storing relays SU and corresponding stopping circuits including selector machine segments 36 for the various fioors which cooperate with selector machine brush 37.

If the car be traveling up and is approaching the highest hall call, assumed to be a down call at the eleventh floor, and has no higher car call to be answered, its high call relay HCR (FIG. 10) is energized so as to open its contacts in line 128, FIG. 3. The high call reverse relay HCR by opening its normally closed contacts HCR in line 128 releases the up direction relay UL in the event the car has no unanswered car call.

FIGURE 3 also shows the circuits for establishing the direction preference of the car in response to car calls and hall calls. Thus as long as there is an up car call registered so that relay contacts CB in line 127 are closed and the car does not then have a down directional preference established and is not at its upper limit of travel, so as to open limit switch contacts 40, the up direction preference relay UL is energized and the car, upon receiving a start signal, will start in the updirection. Likewise if the car has a lower car call registered so as to close its contacts CBD in line 123 and is not at its lower limit of travel, so as to open limit switch 41, and is not engaged in upward travel, as indicated by closure of normally closed contacts UL, the down direction preference relay D1. is energized and the car upon receipt of a starting signal moves downwardly.

This circuit also energizes the directional preference relays upon receipt of signals indicating hall calls ahead which may be either up hall calls indicated by closure of contacts UHC in line 128 or down hall calls indicated by closure of contacts DHC in line 124. Since the up hall call or down hall call indications are canceled when the last hall call in the direction is answered and since it is desirable to maintain the directional preference during the stop a sealing or holding circuit including stop relay contacts S in line 125 and brake and timer contacts BK and TR in line 126 is provided so that the energized directional preference relay UL or DL remains energized while the car is stopping and for a short additional time, e.g., the

customary door open time interval for an intermediate floor.

FIGURE 3 also shows a top zone relay TZ that is energized through a selector machine contact 43 shown in line 121 when the car passes some selected intermediate fioor such as a floor halfway up the building when the car is running up. This relay immediately seals itself in through its contacts TZ and in service relay contacts IS in line 122 and is thus maintained in its energized condition until the car is selected for down travel. The top zone relays are employed in a circuit shown in FIGURE 5 register a call but no stopping signal to call a car to the top zone in anticipation of trafiic from the top zone in the event no up directed car is in the top zone. The call is canceled as the car enters the top zone and, in the absence of any other calls, the car stop at the next floor.

In order that the cars shall not run except on signal and be ready to travel in either direction as needed the directional preference relays UL and DL are deenergized when the car is idle. In the event the car is standing at an intermediate floor with its doors closed and a hall call is registered at that floor that hall call first appears as either an up or a down hall call in the hall call sensing circuit. If the car is selected to be the one to answer the call, i.e. there is no car already approaching the call, its up or down hall call sensing relay is energized to close the cir cuits in lines 113 or 114 to energize a door reopening relay DRO. This relay immediately initiates a door opening and at the start of the door movement the gate relay (door safety) closes its contact G in line 105 to cancel the just registered floor call. The selected directional preference relay remains energized through the timer contact TR so that the passenger has time to enter the car and register his car call before losing the directional preference. However if he delays registering the car call until after the doors have closed the directional preference is lost and the car may then respond to some other hall call in preference to the subsequently registered car call.

As part of the process of selecting cars for loading at the lobby provision is also made to maintain an up direction preference at the lobby once it is established. This is accomplished by the holding circuit completed through lobby floor relay contacts MG and up preference relay contacts UL in line 129. Basement serving cars also have lobby floor contacts MG and car call below relay contacts CBD arranged in line 124 to energize the down preference relay DL if a basement car call is registered in the loading car. The basement call must be registered prior to any up car calls since energization of the car call above relay CB opens its contacts in line 149 to prevent energization of the car call below relay CBD.

FIGURE 4 The circuits for registering car calls, i.e., destination calls, and the circuits for providing car response to such calls are shown in FIG. 4. Car calls or destination calls are registered by car call relays appearing in the center of FIG. 4A at lines 151 to 153 inclusive. These relays are sealed in contact closing position after they are energized through push buttons in lines 151 and 153 and are held in contact closing position until the car answers the call at which time a canceling coil is energized through brush 45. These relays when energized complete circuits in lines 142 to 149 to selector machine segments 50, one for each fioor, that co-operate with a selector machine brush 51 to energize a car stop relay SC at line 137 whenever the car approaches a position corresponding to a depressed car button.

The actual stopping of the car in response to a car call is the same as the stopping in response to a hall call except that relay contacts SC in line 131 operate instead of hall call stopping relay contacts S in line 132.

FIG. 4 also shows the circuits for indicating for each car whether there is an unanswered car call for a floor above or below the car. For this purpose a series of camoperated switches 52 and 53 operated by earns 54 and 55 of the selector machine are provided to connect the car button relay circuits to call above relay CB and call below relay CVD. The normally closed cam operated switches 52 provide a circuit from any energized car call relay contacts for a floor above the car upwardly to a lead 56 that is connected through an operating coil of a car call above relay CB and normally closed down directional relay contacts DL to a supply lead L5. In a similar manner the second series of normally closed cam operated switches 53 provide a series circuit from the energized car call relay contacts to the bottom or lowermost of such switches thence to an operating coil of a car call below relay CBD and through normally closed contacts CB of the car call above relay CB which are connected to the supply lead L5. The earns 54 and 55 are arranged to open the cam operated switches at points in the circuits above and below the position then occupied by the car. Thus, if the car is located at the third floor the cam 54 is arranged to open the second and third switches of the series 52 thereby breaking the circuit from car buttons for floors at or below car position to the car call above relay CB while the cam 55 is arranged to operate the third and fourth switches of the series 53 to break the circuit from car call relays for floors at or above the car position to the car call below relay CBD. Two cams and two series of switches are ordinarily supplied so that any variations of floor spacing may be accommodated.

SUPERVISORY CONTROL FOR VARIOUS TRAFFIC CONDITIONS The supervisory control circuits must operate under a wide variety of traffic conditions. These vary from a condition of intermittent traffic which occurs during the night or on holidays when calls for service may be widely spaced in time to the other extreme of peak traffic conditions when it is diflicult to promptly serve all of the demands for service. The peak trafiic demands may occur in an office building during the start of a business day, during the lunch hour, and during the close of the business day. During the start of the day, most of the traffic is up traflic from a lobby floor, during the noon hour it varies from a heavy down trafiic or peak down trafiic through heavy two way trafiie to up peak trafiic as the tenants leave for the lunch hour and return.

During up peak trafiic conditions, the trafiic may be handled expeditiously if the cars are returned to the lobby floor in response to absence of cars available at the lobby and if each car departs on its upward trip as soon at it is fully loaded or, it another car is at the lobby, as soon as a call is registered and a reasonable time interval elapses without the entrance of a passenger. During periods of heavy down tratfic the circuits are arranged to remember the highest call below a floor at which a down hall call is answered and to limit the service of available or idle cars to those floors below such remembered floors until there are no calls below the last answered call. During light and intermediate trafiic demand intervals, the cars, when not actively answering a hall call or serving a car call, remain at their last stops.

FIGURES 5 and 6 The essential elements and circuits for selecting the cars to respond to ball calls are illustrated in FIGURES 5 and 6. As illustrated these comprise a transmission circuit for the system and a pair of sensing circuits for each car. The transmission circuit is illustrated in detail and the sensing circuits by block diagrams in FIGURE 5. The transmission circuit itself comprises a chain of rectifiers 60 that are connected between segments that comprise up segments 61 and down segments 62 of the floor selector machines for the various cars. Corresponding segments on the 'various machines are connected in parallel. The junctions between the rectifiers, i.e., the segments 61 or 62, are connected through resistors 63 and hall call relay contacts to a power supply lead 64. Each of the cars has a pair of sensors, an up sensor 65 and a down sensor 66, one of which is illustrated in detail in FIGURE 6. The sensors include up brushes 67 and down brushes 68 that cooperate with the selector machine segments 61 and 62 respectively.

Each of the sensors has the characteristic that it accepts current from the segments 61 or 62 in amounts and at voltages that vary according to the condition of loading or status of the car. In general, if a car is in condition to accept a call the input impedance of its sensor is very low so that it acts practically as a short circuit from its brush 67 or 68 to ground. If a car such as a half loaded car is to accept a hall call only in the event there is no other car in a better position to serve the call then the voltage at its brush must rise above a certain threshold level before the sensor will accept any current. This provides the selection of the cars in accordance with the condition of the cars. In actual operation suppose a down call is regis tered at the fifth floor, such that the contacts SSD at line 169 are closed, then current flows from the supply lead 64 through the fifth floor resistor 6-3 thence upwardly through the diodes 60 to the first selector machine segment that is contacted by a sensor brush such as the brush 6%; of the down sensor 66 whose car is shown located at the eighth floor. There is also the possibility that, it the first sensor rejects the signal that, the current may flow on up the circuit to the brush 68 and down sensor 66 of the car shown located at the twelfth floor. The path the current takes depends upon the threshold voltage imposed by the respective sensors. If the car at the twelfth floor has a light load or is in the process of starting to answer a call other than the call at the fifth fioor it is an active car and its sensor has a practically zero threshold voltage level. At the same time the car at the eighth floor may be an idle or reserve car and since it is undesirable to start this car to answer the call at the fifth floor in view of the prospective prompt service by the car coming down from the twelfth floor the threshold voltage level of the eighth floor cars down sensor is set at a voltage which is slightly more than the voltage drop through the rectifiers connected between the intervening floor segments. If by chance the higher car is not in condition to readily accept another call its threshold voltage will be higher so that the current flowing from the fifth floor call will find an easier path through the sensor of the lower car with the result that the lower car will respond to the call.

As is described in connection with FIGURE 6 the amount of current that a sensor accepts or takes from the transmission circuit is limited according to the condition of the car and varies in amount from nothing to that corresponding to two calls. Thus supposing that the system is at rest with the cars in positions as shown and that two down call are registered at floors between the second and seventh. Under this assumed condition the cars at the eighth and twelfth floors are equally available to answer calls and therefore the eighth floor car is preferred. Since this sensor, the car being empty, can accept the equivalent of two calls it maintains an eitcctive ground at the eighth floor selector machine segment 62 so that no current flows to the next car. Thus the first car responds to the calls and is the only car responding to these calls.

Next assume that before either of the calls isanswered a third call is registered below the lower car. This increases the current flow beyond the amount that the lower car sensor accepts and the excess current flows up through the rectifiers to the down sensor of the next above car. Thus the registration of the third call starts a second car in operation.

A preferred form of sensing circuit, such as a down sensor 66 illustrated in FIGURE 6, comprises a pair of transistors Q1 and Q2 shown at line 188 arranged to operate down hall call relays DHCQ and DHC shown in lines 184 and I186. In an up sensor the relays are UHCQ and UHC. The coil of relay DHCQ is in the collector circuit of the transistor Q2 and its normally closed contacts DHCQ control the energization of the coil of the down hall call relay DHC. Signal current for the first transistor Q1 is supplied to its base 71 from its brush 68 when the car is idle or moving down by lead shown in line 188 that includes normally closed car call counting relay contacts CC, load bypass contacts LBP and normally closed up preference relay contacts UL as well as a diode 72. If the car is out of service or on special service its bypass contacts LBP are open. If desired, to limit the rate of voltage rise in the input circuit, a condenser i] may be connected between the brush 68 and ground. Current supplied to the base 71 of transistor Q1 from the transmission circuit by way of the brush 63 flows through its emitter 73, a lead 74 and resistors 75, 76 and 77 to a negative voltage lead '78 that is preferably held approximately 100 volts negative with respect to ground by means of a power supply '79 which may be common to all of the sensors.

Prior to the receipt of a signal, current is supplied from a positive 25 volts supply lead it from a power supply 81, which may be common to all of the sensors, through resistors 82 and 83 to a base 84 of the second transistor Q2. With the first transistor Q1 cutoii, i.e. no signal, the second transistor Q2 draws current so as to energize the coil of the down hall call transistor relay DHCQ by current flow from the lead through the transistor Q2, and through the resistors 75, 7-6 and 77 to the return lead 78. By means of an adjustable resistor 85 this circuit is adiusted so that the potential of the lead 74, which is connected to the upper end of the resistor 75 and to the emitter of the transistor Q2 is held at a positive voltage of three or four volts. The voltage drop through one of the diodes 5d of the transmission circuit is approximately one half volt. Upon the receipt of a signal current from the transmission circuit through the brush 6% the tran sistor Q1 becomes conducting and by drawing current through its collector resistor 82 drops the potential of its collector practically to the potential of the emitter 73 connected to lead 7d. This drop in potential at the collector drops the potential of the base d4 of the second transistor Q2 which is then biased negatively by a bias resistor 86 so that transistor Q2 is cutoff to deenergize its relay DHCQ and at the same time decrease the current flow through the resistors 75, 76 and 77. The potential at lead 74 therefore tends to drop, the potential drop being limited by a diode 37 so that the potential of lead '74 is clamped approximately a half volt negative with respect to ground. This drops the potential of the base 71 of the transistor Q1 and therefore the potential at the brush 68. This drop in potential is momentarily opposed by the condenser 70 whose principal function is to limit a rate of change of voltage at the brush 68. Upon energization of the down hall relay DHC the car receives a down starting signal and proceeds downwardly to answer the call at the floor below.

The positive potential for the lead 64 of FIGURE 5 is provided by a power supply 90 the negative terminal of which is connected to the positive terminal of the 25 volt supply 81.

The amount of current that a sensor can take from the transmission circuit comprising the rectifiers 60 and resistors 63 is limited by the resistors 75, 76 and 77' because any attempt to pass more current causes an increased voltage drop across these resistors thereby cutting otf current flow through the diode 87 and raising the potential of the lead 74 above ground potential. The circuit is preterably adjusted so that if the car has no car calls registered so that contacts CB and GED in lines 191 and 192 are closed and the car is not stopping for a call so that contacts K in line 193 are closed and assuming that the motor generator set is running so that contacts GEN in line 195 are closed to short out the resistor 77 a current equivalent to two calls may flow without materially changing the potential of the lead 74. However if the car has a car call registered or is stopping in response to a hall call the resistor 76 is aiso included in this circuit so that any sub- 1 l stantial current in excess of one call causes a rise in potential on the lead 74.

A biasing resistor d2 in cooperation with a clamping diode 93 is arranged to urge the base 71 of the first transistor Q1 negative so that an input current of approximately of the current corresponding to a call must be supplied before there is a rise in potential on the base of the transistor Q1. This initial current absorbs any leakage in the reverse direction through the diodes 60 in the transmission circuit shown in FIGURE 5.

Since it is undesirable to start the motor generator sets of the elevators unless they are actually needed the contacts GEN shown in line 195 are provided in cooperation with the resistor 77 to increase the resistance of this series of resistors sufiiciently so that with the transistor Q1 cutoff and transistor Q2 drawing current the potential on the lead 74- rises to a value of 12 or volts positive with respect to ground This raises the threshold of the sensor enough so that any calls are refused by the reserve car, the car with its motor generator set shut down, as long as there is another car in the system having its motor generator set running and not having more than two hall calls or a car call and a hall call still to be responded to. If the other cars in the system are busy or are in reserve status the voltage on the selector machine segments 61 and 62 as a result of the registration of the additional call rises sufiiciently to overcome the 15 volt threshold of the closest reserve car so that its hall call relay responds thus giving a starting signal to the car. In response to such a starting signal the car starts its motor generator set and proceeds to answer the call.

The feature that a halt loaded car bypasses hall calls it ahead of an idle or active car is accomplished by the closure of half load contacts HLBP in line 188 to connect the lead 74 through a diode 95 to a junction between a pair of resistors 96 and 97 connected across the power supply 81. This raises the potential of the lead 74 to approximately 5 or 6 volts, this being 2 or 3 volts greater than the threshold voltage for an idle car, so that if there is a closely following active or idle car the current in the rectifier loop circuit of FIGURE 5, the transmission circuit, is diverted from the sensor of the half loaded car to the sensor of the following car. Upon the relative drop in potential at the base of the transistor Q1 with respect to its emitter 73 and the increased potential of lead 74 the transistor Q1 cuts off so as to turn on the transistor Q2 and thus deenergize the down hall call relay DHC of that particular car. This relay by opening its contacts in line 111 opens the circuit to the stop relay S so that the car will not respond to the down hall call but will rather bypass that call leaving it for the following car. if the following car or cars are half loaded or otherwise not in condition to accept the call the voltage at the brush 68 rises at the same time that the potential of the lead 74- is increased to maintain the transistor Q1 conducting and thus maintain the down hall call relay DHC energized so that the car responds to the call.

FIGURE 7 illustrates the input voltage vs. input current characteristics of one of the sensor input circuits. In this figure the input voltage is plotted as a function of the input current Upon the registration of a hall call in the zone between the car and a preceding car the voltage on the brush 68 of the sensor rises, unless there is a current path through another sensor, along the zero current axis until it reaches a threshold voltage indicated by the line A if the car is idle, a threshold voltage indicated by the line B if the car has a moderate i.e. half load, or a threshold voltage indicated by the line C if the car has its motor generator set shut down. If the car is not available for service such that its contacts CC or LBP in line 1&7 are opened the voltage at the brush 68 continues to rise until it is finally limited at a level indicated by the line D when current flows from the brush 68 through a diode 99 to the positive lead 6 of the power supply 81. If the car is already an active car with one call the potential on the lead 74 is slightly negative with rei2; spect to ground, by the voltage drop through the rectifier 87 and there is no rise in voltage at the brush 63 other than the increased voltage drop through diode "i2 and the transistor Q1 and the decrease in voltage drop through diode 87.

The threshold voltages determine whether or not the sensor takes any current from the signal transmission circuit. The threshold voltage, line A, is fixed by the voltage drop through relay coil DHCQ, transistor Q2 and resistors 75. This threshold is dropped as soon as transistor Q2 cuts off upon acceptance of a signal. Threshold voltage level B for a half loaded car is determined by the voltage divider 96, )7 and diode 95. Threshold voltage, level C, is determined by the resistor voltage drops when resistor 77 is included in the circuit (motor generator set shut down). Alternatively, the threshold voltage C for a reserve car could be fixed by a diode con nested in series with normally closed generator contacts between a suitable tap on resistor 96 and lead 74.

Assuming for the moment that the car is idle, i.e., has no car calls and is not responding to a hall call and there is no closely adjacent active car, then, as the hall call is registered, the voltage rises to the threshold level indicated by the line A and current flows from the brush 68 through the transistor Q1 and through the lead 74 and resistor 75. As mentioned before this current flow through the transistor turns the transistor Q1 on and turns the transistor Q2 off to drop out the relay DHCQ and also drop the potential on the lead 74 so that the voltage input to the sensor immediately drops to the base line G. The current for one hall call corresponds to a distance out along the base line to a point 101. If a second call is registered at this time the current merely increases to a point Hi2 corresponding to two calls there being a slight but insignificant increase in voltage at the input terminal and the brush 68. However, if a third call is registered the input voltage follows a line H, representing the increase of voftage at the brush 68 because of the cutting off of the current through the diode 87 and the forcing of the additional current through the resistor 75 and the closed contacts CB, CBD, F, and GEN. Actually the voltage rises along the line H only far enough to supply enough voltage to divert the additional current flow corresponding to the third call through the chain of rectifiers 60 to the brush 68 of the sensor of a following car. If there is no available car the voltage rises to a level sulficient to start a reserve car.

As the car answers the first call and cancels the hall call it also energizes its relay Kin line 109 of FIGURE 2 at the same time that the hall call is canceled. The relay K, by opening its contacts in line 193, inserts the resistor 76 into the current limiting circuit thereby cutting the current acceptance of the sensor back to that corresponding to a line I which indicates that the voltage rises as soon as the signal current into the sensor slightly exceeds that corresponding to one call. The relay K, used for call compensation, is necessary particularly in the situation when three calls have been registered in the zone ahead of the car such that the car accepts two of the calls and the third call is diverted to a following car. If that third call is the only call to which the following car is responding, then in the brief interval after the first car has canceled the first call and before a car call is registered in the car in response to that hall call the first car takes all the current from the transmission circuit corresponding to the remaining two calls leaving none to be diverted to the second car. Without the call compensating relay K in this situation the second car would lose its signal and would stop at the next fioor whether there were a call there or not. To prevent this the call compensating relay K, which is energized at the same time that the hall call signal is canceled as the first car answers the call, opens its contacts in the sensor circuit of the first car to reduce its current acceptance from two calls to one call. Since there are two calls remaining ahead of the car the first car thus accepts or takes a current corresponding to slightly more than one of the remaining calls and diverts, by the increase in voltage as represented by the line I, current to the second car thereby maintaining it in operation.

Referring again to FIGURE 6 another feature of the control system is the selection of cars other than the load car at the lobby to answer up hall calls. This is provided by serially connected contacts of a lobby floor relay MG, normally closed contacts of the car call above relay CB and normally open up directional preference relay contacts UL arranged, in line 189, in parallel with half load contacts HLBP in line 188 so that a load car standing at the lobby and not having received any car calls for travel above has its threshold voltage raised to the level corresponding to that of a half loaded car. This is done so that an up call in a lower portion of the building will start a second car from the lobby or call another car down from a higher portion of the building in preference to starting the lobby car. As soon as the lobby car receives a car call its car call above relay CB is energized to open its contacts in line 189 to disconnect the circuit through the rectifier 95. When the car was selected as the lobby load car its up preference contacts UL, line 186, opened to in sert resistor 109 into the coil circuit of the down hall call transistor relay DHCQ so that the potential of the lead 74 drops to that determined by the diode 87. This transfers any registered up hall calls to the lobby car to be answered during its up trip. It may be noted that the circuit including the contacts of the first floor relay MG, the car call above relay CB, and the up direction relays UL need be included only in the sensor for up hall calls.

Selection of cars for basement service when less than all of the cars can serve the basement is provided by a circuit from the positive lead 64 through basement hall call relay contacts SBU or first floor down hall call contacts S1D at lines 181 and 182, a resistor 107, and separate diodes 108 to the inputs of the down sensors of each of the basement serving cars. Whichever car has the lower input threshold voltage accepts the signal and travels down. If the resistor 107 has a resistance a little less than half that of one of the resistors 63 the current flow is suflicient to raise the potential of the lead 74 and thus divert any other hall call signals to another car.

When a car is running in response to a car call and no hall calls are registered the resistor 76 is in circuit and the sensor has a high threshold voltage level. To reduce this level the resistor 109 is also introduced into the circuit. This is adjusted to drop the potential on the lead 74 to ground potential so that the sensor may accept a hall call signal rather than pass the signal to another car.

FIGURE 8 The car starting circuits and in particular the circuits for energizing its car start relay CS when the car is to respond to a call are illustrated in FIGURE 8. As shown in this figure the car start relay CS is energized whenever there is either a down hall call ahead, an up hall call ahead, an up car call above or a down car call below as indicated by a closure of any one of the contacts DHC line 211 for down hall calls, UHC line 212 for up hall calls, CB line 213 for car calls above and GED line 214 for car calls below. The actual car start is delayed for at least a minimum time interval by timing relay contacts TR that close a short predetermined time after the doors have reached fully open position or after a passenger has passed through the door. If desired the TR contacts may be included as part of a standing time saver relay assembly such as shown in Patent No. 2,758,676, arranged so that the doors remain open and the car start delayed for a certain period of time in the neighborhood of 3 or 4 seconds following the" opening of the doors which time is cut to a shorter time of one-half second whenever a passenger enters the car. Longer time intervals are required at the lobby floor and in particular it is desirable that the car wait after the registration of its first car call until there is either another car at the lobby or enough passengers have entered so that it is fully loaded, or that a given interval of time in the order of 15 or 20-seconds elapses after the first car call is registered. The starting circuit, therefore, is opened when the car is at the lobby floor by opening of normally closed contacts MG and is completed to start the car by closure of load switch contact LS, shown in line 211, when the car acquires a full load, or by closure of down lobby car contacts DLC when there is another car available at the lobby, or by the closure of auxiliary timing relay contacts TRl which close at the end of a predetermined time in the order of twenty to thirty seconds. The first floor contacts MG are closed as long as the car is not at the lobby so that the longer timing intervals are in effect only at the lobby floor.

As indicated the minimum time relay TR, line 216, is energized as long as the car is running or opening its doors.

FIGURE 9 The circuits for automatically calling cars to the lobby and selecting the cars at the lobby is illustrated in FIGURE 9. As shown in this figure three relays are involved these being a down lobby car relay DLC shown in line 220', an auxiliary relay R, and a load car relay LC shown in line 222. While the circuits for two cars only are shown these circuits are connected in parallel and are repeated for each of the other cars. A car approaching the lobby floor closes its lobby floor relay contacts MG, shown in lines 220 or 223, just prior to its brush 68 leaving the second floor segment 62 and unless immediately selected for up travel has its normally closed UL contacts closed to complete a circuit to the down lobby car relay DLC. Thus this relay DLC is energized as long as there is a car standing at the lobby and not selected for up travel. A lobby car relay LC and an auxiliary relay R are energized as long as any car at the lobby is set for up travel, the relay R being released or deenergized when a car call is registered in the up car. When the up car departs and opens its first floor contacts MG the load car relay LC drops out thereby closing contacts LC at line 174 and opening contacts LC in line of FIGURE 5 thus energizing the up hall call sensor of the other car at the lobby. As soon as this sensor is energized by this signal it energizes its up hall call relay UHC (corresponding to the down hall call relay DHC shown in FIGURE 6 of the down sensor) thus closing its up hall call relay contacts UHC in line 128 to energize the up direction memory relay UL for the car. It also closes its contacts in lines 221 or 224 to energize the lobby car relay LC thereby opening the contacts LC in line 174 of FIGURE 5. A first floor up signal is also supplied by contacts LC in line 118 so that the car opens its doors if they had previously closed, lights its load light to signal any prospective passengers at the lobby and awaits the entry of any passengers. As long as no car call is registered in the loading car the relay R is also energized to open its contacts at line 173.

If there is no down lobby car at the lobby, the relay DLC is deenergized to close its contacts in line 173 to prepare a circuit to the second floor down signal transmission segment 62. This circuit is completed as soon as a car call is registered in the up lobby car by deenergiz-ing the R relay at line 221. This circuit in line 173 supplies a down hall call signal at the second floor but no stopping signal for the floor. The lowest available car, in response to the signal transmitted up through the chain of rectifiers, moves down, runs past the second floor, and loses its down signal as it passes the second floor while moving toward the lobby. Upon the loss of this signal with no calls registered it loses its directional preference and completes its stop circuit, shown in line 134 of FIGURE 4, to cause the car to stop at the next floor, namely the lobby floor, without any directional preference. This car thus becomes the down lobby car and is available for up service as soon as the loading lobby car leaves.

In the event there are two or more cars at the lobby in addition to load car the selection of the next load car is made according to the individual sensitivities of the up hall call sensors for the various cars since the car with the lowest threshold will take the signal current leaving none for the sensor of the other car. The opening of the contacts LC in line 175 confines the signal current to the cars at or below the lobby. It may be noted from line 129 of FIGURE 3 that as soon as a car is selected for up travel and is standing at the lobby a sealing circuit is completed to its up memory relay UL to maintain the directional preference for this car after the hall call signal supplied through the normally closed LC contacts to the sensor disappears as the lobby car relay LC is energized. This circuit thus calls another car to the lobby whenever there is only the load car at the lobby and a call is registered in the load car indicating that it will soon depart. To maintain the service at the lobby the load car is detained after the registration of the first car call until either a maximum time interval elapses or another car arrives at the lobby. Therefore, while a passenger enter ing the load car may have to wait a few moments the car departs as soon as it possibly can without detriment to the upservice at the lobby.

During periods of heavy up traflic it is desirable to return the cars as soon as possible and this is accomplished in this control system by providing car call counting relays CC, as shown in line 159 of FIGURE 4A, responsive to the current flow through the energized car call relays and adjusted to operate as soon as a predetermined number such as three car calls are registered in the car. As soon as three such calls are registered in a car the corresponding call counting relay closes its contacts in lines 174 or 175 of FIGURE 5 to supply a down hall call signal to the transmission circuit at the second floor point. This second floor call is maintained regardless of the response of the cars until there is no up car having three or more car calls registered. By making the value of a resistor 119 equal to approximately 20% of one of the resistors 63 sufiicient current may be supplied to the trans-mission circuit to insure the starting of reserve cars in the system thus promptly starting all of the cars and returning them to the lobby floor in anticipation of the remaining up trafiic.

A somewhat closer balance between the number of cars called into service and the demand may be made by increasing the resistance of the resistor 110 so that the current supplied to the down hall call transmission circuit when any car has three or more up car calls registered results in a signal current equal to that of one hall call. This is sufiicient to start any reserve cars in the event there are no idle or active cars available. It may be noted that the sensors of any car having three or more car calls registered are disconnected from the transmission circuit by the opening of the car call counting relay contacts CC in series with the brushes 67 or 68. Thus if all of the cars in service, which is assumed to be less than the total number of available cars, have three or more car calls registered in each there are no available cars and the nearest reserve car is immediately started. If this car arrives at the lobby and receives its load of three or more car calls prior to the reversal of any of the up traveling cars still another reserve car is started and so on until enough cars are in service to supply the demand. It may be noted from FIGURE 4A that the car call relays C3, C7 and so forth are reset as soon as the call is answered. However the car call counting relay may have its pickup current adjusted for three or more calls and its dropout current adjusted for less than one call so that once it is energized for a particular up trip it remains energized until the last call is answered.

FIGURE 10 The improved circuits are also adapted to detect heavy down peak traffic conditions when there are more down calls than there are cars vailable to answer them. When this condition occurs the voltage of the down segments 62 of the transmission circuit of FIGURE 5 rises until current flows through one or more of a group of diodes connected to spaced apart ones of the segments 62, a break down or Zener diode 131 and resistor 132 connected to ground. The voltage developed across the resistor 132 is transmitted through a resistor 133 to a base 134 of a transistor Q3. A sweeping relay SW is connected in the collector circuit of the transistor Q3 to be energized in response to the voltage rise in the transmission circuit. The transmission circuit voltage required to operate the sweeping relay SW is indicated by a line K in FIG. 7 intermediate the lines C and D. This voltage is greater than that required to start a reserve car and less than that required to pass current through the diodes 99 of the sensors.

When the sweeping relay SW is energized it starts a sweeping cycle of operation. During a sweeping cycle the upward travel of each car is limited to a high call reverse ceiling which is initially at the highest call in the building and which drops to the next highest call in registration as the call at the ceiling is answered. The ceiling thus progresses downwardly through the building and starts over at the top when the lowest calls are answered.

The circuit shown in FIG. 10 to provide sweeping comprises a conventional high call reverse circuit including normally closed contacts of the hall call relays and selector machine segments for each floor on each floor selector machine. The segments 140 for each floor are connected to power supply lead L1 through a lead 141 and normally closed contacts of all the hall ca-ll relays for the floors above and including the up hall call relay for that floor.

A high call reverse relay HCR for each car has a brush 142 cooperating with the segments 140 so that the relay is energized as long as there are no hall calls above.

The sweeping function is provided by a two deck stepping switch STR having two more step positions than there are floors above the lobby. A first wiper 143 of the stepping relay is arranged to cooperate with contacts 144 that are connected to the junction points in the high call reverse circuit that are also connected to the segments 140. This wiper 143 is also connected to a supply lead L1 that supplies the upper end of the high call reverse circuit. A second wiper 145 of the stepping relay cooperates with a series of contacts 146 of the second deck of the stepping relay, these contacts being connected individually to the contacts 144 of the first deck corresponding to the floor immediately below. Thus, for example, when the wiper 143 cooperating with the contacts 144 of the first deck is at the position corresponding to the 16th floor the wiper 145 cooperating with the contacts 146 is at the contact corresponding to the 15th floor i.e., one floor below. The wiper 145 is connected through self-interrupting contacts STR of the stepping relay and the operating coil STR of the stepping relay to the return line L2. The stepping relay STR is shown in its rest or home position. Whenever the sweeping relay SW is energized as the result of excess down calls it closes its contacts SW in line 241 of FIGURE 10 thereby energizing the stepping relay through its wiper 145 causing it to advance one step. This moves the wiper 145 to the contact 146 for the 15th floor and the wiper 143 to the 16th floor contact 144. If there is no down call at the top floor and no up call at the next floor the stepping relay STR is again energized through the high call reverse circuit between the top and next to top floors and the wipers move to the next position .at which the wiper 143 energizes the 15th floor segments and the wiper 145 is connected to the next lower segments. T'his stepping continues until a floor is reached at which a call is registered so that upon the completion of the step the stepping relay coil is not again energized. That particular floor then is remembered as the high call reverse ceiling, since the wiper 143 then contacts and energizes the high call reverse circuit at that floor regardless of the subsequent registration of higher hall calls. When the call at that floor is answered the stepping relay immediately steps u til it finds the next call and waits at that position until the call is answered. This continues until there are no remaining calls below the switch position. It then advances to the home position and starts a new cycle it the sweeping relay SW is still energized.

A feature of the supervisory control circuit is that a down traveling, half loaded car does not answer the call at the high call reverse ceiling but bypasses that call and completes its load from lower calls. This is done so that a call at the ceiling will not be canceled and the ceiling shifted by a nearly loaded car unable to take all of the intending passengers.

This is accomplished by the circuits shown in lines 110 and 112. As soon as a car acquires a half load its half load bypass contacts HLBP in line 112 open. The parallel circuit in line 110 including up hall call contacts UHC and up direction contacts UL is open since the car is traveling down. Also the parallel circuit in line 111 including down hall contacts DHC, down direction contacts DL and high call reverse contacts HCR opens a the car approaches the high call reverse ceiling fioor and the high call reverse relay is energized. Thus the car bypasses this call at the ceiling. The high call reverse relay drops out as the car passes the ceiling floor and the car answers the next down call.

SUMMARY The circuits as just described automatically select Cars in response to the registration of hall calls to provide reasonably prompt service to all registered hall calls and at the same time minimize the travel of the elevator cars. During periods of intermittent and light or medium trafiic cars are maintained, one in the upper zone of the building and at least one at the lobby floor. The remaining cars of the system remain standing at whatever floors they reach in serving their last calls for service. In the preferred form of the control circuit cars are called into service at the rate of one car for every two calls. The circuit provides means during the transition from intermittent to heavy up traflic for selecting and starting reserve cars as needed to meet the trafiic demands. In general, a car is started in operation Whenever there is a call registered in a zone ahead of the car and there is no car immediately following and already in motion in that direction. Furthermore if more calls are registered in a zone ahead of a car than it can promptly answer, a signal is directed to the next car in order so that it may immediately come to the assistance of the car having the excess hall calls ahead of it.

This feature of the control circuit maintains a reasonable balance between the number of cars in operation and the trafiic demands at that particular moment. During periods of heavy down traffic the circuits provide by sweeping that no floor will receive service twice while there are previously registered calls remaining unanswered at lower floors except that floor calls answered by half loaded cars may receive service a second time if a call is reregistered promptly after the departure of the half loaded car. Actually these are calls below the high call reverse ceiling that are answered by a car that bypassed the call at the ceiling and the call at the ceiling has not been answered by another car prior to the reregistration of the call at the lower floor. During periods of heavy down traffic the floors receive service in systematic order and the chances of leaving passengers stranded by reason of answering calls with heavily loaded cars is iinimized.

Bunching of the cars, the condition in which the cars tend to travel together, does not occur in this system because a car does not start until there is a call registered behind a preceding car or there is an excess number of calls ahead of the preceding car. Since the latter condition 18 does not occur very often and since the calls for service are usually randomly spaced the cars are maintained in spaced condition and there is thus prompt service to all of the calls.

Having described the invention I clalmz 1. A group supervisory control system for a group of elevator cars arranged to serve a plurality of floors comprising, in combination, means for registering calls, a call transmission circuit common to a plurality of elevator cars of said grOup and corresponding to the path of-the cars connected to said call registering means, a unidirectional conductive device having a forward voltage drop in said transmission circuit for each position corresponding to a floor along the path of the cars, means for supplying a substantially constant direct currentto said transmission circuit at points corresponding to registered calls, current sensing means for each car connected to said transmission circuit at points corresponding to the position of the car, said sensing means being adapted to drain current from said circuit in a magnitude which is a function of the availability of the car to answer calls whereby the sensing means of the available car most proximate a point corresponding to a registered call alters the current in said transmission circuit from said point to the sensing means of other cars, and means for starting each car in response to the acceptance of current corresponding to a call by its sensor.

2. A group supervisory control system for a group of elevator cars arranged to serve a plurality of floors, comprising, in combination, means for registering hall calls, a hall call transmission circuit common to all elevator cars of said group and corresponding to the path of the cars connected to said call registering means to receive and transmit signals corresponding to registered calls, a unidirectional conductive device having a forward voltage drop in said transmission circuit for each position corresponding to a floor along the path of the cars, means for supplying a substantially constant direct current t said transmission circuit at points corresponding to the floor positions for which hall calls are registered, a signal receiver for each car that is connected to the transmission circuit at a point corresponding to the position of the car, means for each signal receiver to establish an upper limit for a signal acceptance level corresponding to the service conditions imposed upon its car which aiTect its capacity to promptly serve calls for service of its car to limit its acceptance of signals in said transmissions circuit from hall calls to those that its car may promptly serve, said signal receiver being adapted to drain current of a magnitude up to that of said limit means from said circuit whereby the signal from said circuit to the signal receivers of other cars is reduced, and means connected to the signal receiver of a car adapted to start the car in response to the acceptance of a signal corresponding to a call from the transmission circuit.

3. In an elevator system comprising a plurality of cars serving a plurality of floors, in combination, means for registering calls for service, a transmission circuit common to said plurality of cars and analogous to the path of the cars, means for transmitting signals to said circuit corresponding to such calls for service, means for each car for accepting current flowing in said circuit corresponding to calls that the car can promptly answer and simultaneously shunting signal current corresponding to further calls to the sensing means of other cars, and means for operating the car in response to sensed signals.

4. In an elevator system comprising a plurality of cars serving a plurality of floors, in combination, means for registering calls for service, a signal transmitting circuit, means for transmitting signals, a signal transmission circuit common to said plurality of cars and corresponding to the path of travel of said cars, corresponding in a spatial relationship in said circuit to the floors at which are registered such calls for service, means for each car for sensing the signals in said circuit coresponding to calls ahead of the car, means for operating the car in response to the sensed signals, means responsive to the registration of a call in a car at a particular floor at which a car is to be maintained for calling another car to such floor, and means responsive to the registration of a predetermined number of calls in a car traveling away from such particular floor adapted to start still another car toward such particular floor.

5. In an elevator system comprising a plurality of cars adapted to serve a plurality of floors, in combination, means for moving the cars in response to demands for service, means for registering calls for service, a signal transmitting circuit common to the plurality of cars and analogous to the path of the cars connected to said call registering means with each registered call tending to raise the signal level in the transmitting circuit at a location corresponding to the floor for which said cell is registered, a signal receiver for each car, means for each car for adjusting the threshold of response and the signal receiving limit of said receiver of said car according to the service conditions imposed upon the car which affect its capacity to serve promptly calls for service, each signal receiver being connected to and adapted to reduce the signal level in said transmitting circuit at a position corresponding to the car position to a level determined by the signal receiving limit established by said adjusting means of the car, said transmitting circuit being adapted to modify the level of transmitted signals from point to point corresponding to floors along said path of said cars, each sign-a1 receiver being adapted to provide an operating signal to its car when the signal level tends to exceed the threshold of response determined by the said adjusting means of the car, whereby calls for service are continuously distributed individually to the cars individually in accordance with their positions and imposed service conditions.

6. In an elevator system comprising a plurality of cars adapted to serve a plurality of floors, in combination, means for moving the cars to serve calls for service, means for registering calls for service, at least one signal receiver for each car, each signal receiver having a threshold receiving level that varies with the availability of the car,

a signal transmitting circuit that is connected to the call registering means at points corresponding to registered calls and to the signal receivers at points corresponding to the positions of the cars, the signal receivers of at least some of the cars having a threshold receiving level when the motor generator sets of the cars are idle that exceeds the maximum loss in signal level in the transmitting circuit, whereby the signal receiver of a car having an idle motor generator set responds to signals only when there is no other car in the system available to answer a registered call.

7. In an elevator system comprising a plurality of cars adapted to serve a plurality of floors, in combination, means for moving the cars to serve calls for service, means for registering calls for service, a signal transmission circuit common to the cars for transmitting signals corresponding to calls for service, at least one signal receiver for each car, each signal receiver being connected to the transmitting circuit at a point corresponding to the position of the car, each signal receiver having a threshold receiving level that differs slightly from the level of signal receivers of other cars and that varies with the service conditions imposed upon the car which affects its capacity to promptly serve calls for service and that decreases as the car accepts a call for service whereby only one of a plurality of cars of equal position and imposed service conditions is selected to respond to a call for service.

References Cited UNITED STATES PATENTS 2,100,176 11/1937 Waters et al 187--29 3,256,958 6/1966 Savino et al. 18729 3,292,736 12/1966 Savino et al. 187-29 2,836,262 6/1958 Hockstein et al. 18729 2,861,653 11/1958 Burgy 187-29 3,185,932 5/1965 Walker 330l2 3,063,020 11/1962 Horowitz 330-12 2,827,981 3/1958 Eames et al. 187-29 2,886,137 5/1959 Lund et al. 187-29 ORIS L. RADER, Primary Examiner.

THOMAS LYNCH, Examiner. 

1. A GROUP SUPERVISORY CONTROL SYSTEM FOR A GROUP OF ELEVATOR CARS ARRANGED TO SERVE A PLURALITY OF FLOORS COMPRISING, IN COMBINATION, MEANS FOR REGISTERING CALLS, A CALL TRANSMISSION CIRCUIT COMMON TO A PLURALITY OF ELEVATOR CARS OF SAID GROUP AND CORRESPONDING TO THE PATH OF THE CARS CONNECTED TO SAID CALL REGISTERING MEANS, A UNIDIRECTIONAL CONDUCTIVE DEVICE HAVING A FORWARD VOLTAGE DROP IN SAID TRANSMISSION CIRCUIT FOR EACH POSITION CORRESPONDING TO A FLOOR ALONG THE PATH OF THE CARS, MEANS FOR SUPPLYING A SUBSTANTIALLY CONSTANT DIRECT CURRENT TO SAID TRANSMISSION CIRCUIT AT POINTS CORRESPONDING TO REGISTERED CALLS, CURRENT SENSING MEANS FOR EACH CAR CONNECTED TO SAID TRANSMISSION CIRCUIT AT POINTS CORRESPONDING TO THE POSITION OF THE CAR, SAID SENSING MEANS BEING ADAPTED TO DRAIN CURRENT FROM SAID CIRCUIT IN A MAGNITUDE WHICH IS A FUNCTION OF THE AVAILABILITY OF THE CAR TO ANSWER CALLS WHEREBY THE SENSING MEANS OF THE AVAILABLE CAR MOST PROXIMATE A POINT CORRESPONDING TO A REGISTERED CALL ALTERS THE CURRENT IN SAID TRANSMISSION CIRCUIT FROM SAID POINT TO THE SENSING MEANS OF OTHER CARS, AND MEANS FOR STARTING EACH CAR IN RESPONSE TO THE ACCEPTANCE OF CURRENT CORRESPONDING TO A CALL BY ITS SENSOR. 